Cable Television (CATV) is a form of broadcasting that transmits programs to subscribers via a physical land based infrastructure of coaxial (“coax”) cables or via a combination of fiber-optic and coaxial cables (HFC).
Traditionally, analog services providing CATV content have been carried over an electronic signal having a frequency range (band) of about 75-500 MHz. Typically, the legacy frequency band of about 5-42 MHz is dedicated to upstream transmissions sent from subscribers of the CATV networks to a cable network head end. CATV operators must continue to provide analog contents within analog channels for economic, regulatory, and legal reasons. As a result, about 130-450 MHz or the 130-550 MHz frequency band remains dedicated to the transmission of the traditional analog channels. The recent advent of technology requires the suitable expansion of the transmission spectrum or the frequency bandwidth of carrier signals sent and received across the physical distribution path.
In some modern CATV networks, e.g., some CATV networks implemented in the U.S.A. as well as in certain other countries, a legacy frequency band of approximately 5-860 MHz is used. A large portion of the frequency band, e.g., a frequency bandwidth of between 700 MHz and 800 MHz, is generally used for legacy downstream transmissions from the cable head end equipment to the subscriber, while a relatively narrow portion, e.g., less than 40 MHz in the US and less than 60 MHz in Europe, is generally used for upstream transmissions between the subscriber and the head end. Until lately, this asymmetry had not been a concern due to the prevailing transmission needs of upstream traffic. Typically, upstream traffic comprised subscriber-submitted requests involving subscriber demands for the reception of video programs, music programs, live radio transmissions, data files, multi-media content, applications, and the like, in the downstream. The volume of these files has been typically much higher than the volume of the respective requests. As a result early proprietary cable modem systems and the subsequent Data Over Cable Service Interface Specification (DOCSIS) called for spectrally efficient modulation schemes in the downstream path and relatively low-rate but robust schemes in the upstream path. Recent trends suggest that data, as well as voice and video traffic over HFC networks is becoming gradually more symmetric as certain applications and services demand using an upstream channel having a relatively wide upstream bandwidth. However, the upstream channel of the typical CATV networks is relatively narrow and cannot supply the demand for upstream traffic even if such upstream traffic is compressed.
The present alternatives, such as the use of Fiber-optic To The Home (FTTH) last-mile networks, are expensive and require replacing/modifying the standard subscriber end devices with devices specifically designed to operate in such networks. In addition, the 5-42 MHz (or 5-65 MHz in some countries) frequency band, which is utilized as the upstream path, is heavily affected by ingress noise. Ingress noise in a CATV network is typically generated by the operation of electric household devices as well as other EMI, RFI pick-ups in the vicinity of the drop system and the subscriber premises. Ingress noise is especially critical at the lower frequencies. Because currently the only portion of the transmission spectrum used for the upstream path is the 5-42 MHz or the 5-65 MHz frequency band, ingress noise is a dominant problem for the CATV operators attempting to implement two-way services. The result is that less than 20 MHz can be operatively used for efficient high-speed data transmission in the upstream path due to the noise funneling effect of the upstream path. It is becoming widely accepted that a large percent of ingress noise problems stem from a drop system (drop and subscriber premises) of the network, and only a small percent of ingress noise originates in the trunk and feeder network. In addition, a hard line of the feeder network is typically well shielded and better maintained, whereas the drop system generally has lower shielding and/or isolation quality. Furthermore, the drop system is generally the least accessible, least controllable and least maintained portion of the network. In an effort to speed the activation of the reverse plant, many CATV operators currently install high-pass filters and windowed filters at the subscriber end, e.g., in each and every user's home. Unfortunately, although such filtering methods may be fairly effective and affordable, heavy reliance on filtering can be only a limited and/or temporary solution.
Persistent commercial competition between CATV operators and Satellite (DBS) and/or Telephone Operators (Telcos), requires the continuous improvement of the services provided to their subscribers, such as the addition of new video and audio channels, more flexible programming, more symmetrical data transfer capabilities, telephone and video services over cable, T1/E1 type performance that requires guaranteed symmetric bandwidth, multi-user games over CATV networks, video telephony that requires symmetrical bandwidth, and other advanced services. The above-mentioned limitation concerning the availability of the bandwidth for digital services may hinder the ability of the CATV operators to compete successfully on today's extremely dynamic market where new cable network-related services are being developed and implemented continuously and new requests are made constantly by the increasingly sophisticated customer base concerning the enhancement of the desired programming mix. This results in an ever-growing need for a wider bandwidth.